1. Technical Field
The present invention generally relates to vapor deposition of polymer films. More particularly, the present invention relates to increasing the rate of vapor deposition polymerization of such films by application of an electric field.
2. Background Information
Polymer films are commonly used to provide dielectric layers in fabrication of semiconductors. One material typically utilized for such a film is Parylene-N or PA-N, and may be applied to a semiconductor substrate or wafer using a conventional vapor deposition polymerization (VDP) technique. Powder di-p-xylylene (dimer) is typically used as the source material or precursor. The dimer molecules are vaporized and then decomposed into monomers by pyrolysis at a temperature of 650.degree. C. The monomers are finally condensed and polymerized on the substrate such as a Silicon (Si) wafer at room temperature. The reaction process is schematically shown as: ##STR1##
Generally, in order to get a quality polymer film by VDP, a relatively low deposition rate must be used. For example, under conventional conditions, the deposition rate to make quality PA-N films is 50-70 angstroms per minute at 50 milliTorr (mTorr). While the deposition rate may be increased by increasing deposition pressure, pressures generally cannot exceed approximately 80 mTorr without an attendant degradation in film quality, as manifested by a reduction in film clarity. A higher deposition rate tends to cause problems such as unpolymerized films, very short chain polymerization, opaque films mixed with dimer, soluble film, and very low molecular weight films.
However, slow deposition rate for VDP tends to have its own drawbacks. Such problems primarily entail relatively high manufacturing costs, but may also include lowered film quality due to a greater opportunity for reaction with oxygen and contamination by other impurities such as water vapor. Such contamination may affect the electric, thermal and optical properties of the resulting films.
A need thus exists for increasing the deposition rate of VDP without associated loss in film quality.